A technology for reduced-cost photovoltaic modules involves the growth of thin-film polycrystalline silicon on substrates other than silicon wafers. Although the efficiencies of thin-film polycrystalline solar cells are lower than those of crystalline silicon solar cells, production costs are significantly lower as well and they are scalable for large area deposition. Thin-film polycrystalline cells also eliminate some of the quality constraints placed on monocrystalline material which may require costly processing steps, since the minority carrier diffusion length in the polycrystalline film need only be greater than its thickness.
Large-grained polycrystalline silicon material may be fabricated more cheaply than monocrystalline silicon by high-throughput processes such as casting or directional solidification to produce multicrystalline ingots. Although the majority and minority carrier properties of large-grained polycrystalline silicon are close to those of monocrystalline silicon, it has been shown that the presence of grain boundaries decreases the efficiencies of solar cells (due probably to large recombination rate) fabricated using this technology.
Because the open circuit voltage of polycrystalline cells increases with the grain size of the polycrystalline silicon above 1 μm, polycrystalline silicon thick films with a grain size equal to or greater than 1 μm are particularly desirable. Processes which enable deposition on low-cost substrates such as glass would be particularly desirable. When using a glass substrate, however, it is often desired that the temperature of the cell and/or substrate during silicon growth be kept at or below the transition temperature of the glass.
In certain example embodiments of this invention, there is provided a photovoltaic device (e.g., solar cell) comprising an absorber film (made up of one or more layers) comprising polycrystalline silicon having an average grain size equal to or greater than 1 μm.
According to an aspect of an exemplary embodiment, there is provided a substrate (e.g., glass or mica substrate) including nickel inclusive nanoparticles on the substrate, and a nickel inclusive catalyst thin film coated on the substrate which may be deposited before and/or after the catalyst thin film, wherein the nickel inclusive catalyst film may be of or include nickel optionally doped with phosphorus or the like. Heat treating and exposure to gas comprising silane may be used in forming a film of or including polycrystalline silicon.
In certain example embodiments of this invention, there is provided a method of manufacturing a polycrystalline film comprising silicon on a substrate, the method comprising: depositing a catalyst layer comprising nickel, and depositing nanoparticles, on the substrate; exposing the catalyst layer and the nanoparticles to silane gas; and heat treating the substrate coated with the catalyst layer and the nanoparticles during at least part of said exposing to silane gas, in growing a film comprising silicon on the substrate.